Question-

A solenoid is created by wrapping a L = 90 m long wire around a hollow tube of diameter D = 4.5 cm. The wire diameter is d = 0.9 mm. The solenoid wire is then connected to a power supply so that a current of I = 9 A flows through the wire. 

Randomized Variables
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L = 90 m
D = 4.5 cm
d = 0.9 mm
I = 9 A 

Part a) Write an expression for the number of turns, N, in the solenoid. You do not need to take into account the diameter of the wire in this calculation.

Part b) Calculate the number of turns, N, in the solenoid.

Part c) Write an expression for the length of the solenoid (L2) in terms of the diameter of the hollow tube D, assuming it is constructed by using only 1 layer of loops (note that most solenoids are really constructed with many layers, to maximize the magnetic field density).

Part d) Compute the length of the solenoid (L2) in meters.

Part e) Compute the magnitude of the magnetic field at the center of the solenoid in Teslas.